This printer does not support borderless Printing.
Specifications > Paper Handling > Print Margins
That being the case, you will always have at least a small border around your photos.
The issue you are seeing in your example, that is, the odd, larger border on one side of the photo is there because the shape of your photo is not the shape of the paper - that is, this photo does not fit on this paper properly.
This is the Aspect Ratio - the shape of the image as opposed to the shape of the Media (paper) on which you wish to place your image.
You need to crop the photo into the correct shape for your paper to have the photo "fit exactly" as intended. Remember that your photo will still have a tiny boundary around it -- this is a printer restriction and not something you can "edit out" of the image.
If / When you edit the photo to make it the right shape for your paper, then the photo will at least be centered and look "right" on that paper.
You can then adjust the print margins to the minimum for your printer and then print the photo.
In the example shown in the document, it was only necessary to shave a bit off the top of your original photo to make it a better shape for the 4X6 inch paper. That means, I used Paint to remove a rectangle of unneeded sky and rock from along the top of the photo -- now it fits onto the paper you want to use.
Note the word test -- I did not PRINT the image - I used it for the document and explanation.
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